Apparatus for attaching filaments to electrodes in machines for coating with metal vapors



May 5, 1953 z. M. SHAPIRO 2 APPARATUS FOR ATTACHING FILAMENTS T0ELECTRODES IN MACHINES FOR COATING WITH METAL VAPORS Filed Nov. 20, 1951&

1.|||||1|||l|||||.|||1||| IIIIJV Juventor ZALMAN M .S'wzxo Qltorneg-Patented May 5, 1953 UNITED STATES PATENT OFFICE APPARATUS FOR ATTACHINGFILAME'NTS TU ELECTRODES IN MACHINES FOR GOAT- ING WITH METAL VAPORSZahnan .B Shapiro, Pittsburgh, Pa, assignor, by mesnc assignments, tothe United States of America as represented by the United States AtomicEnergy Commission dpplicationl'icvember 20, 1951, Serial No. 257,308

10 Claims. 1

This invention relates to thwart of precipitating metals by thermaldecomposition .of a compound thereof and more particularly to a new andimproved apparatus for mounting the filament or starting wire'whichplays an essential role in the precipitation process. For purposes ofillustration, the invention is described herein being especial utilityin the thermal decomposition of zirconium iodide for the production ofdeposit of zirconium crystal bar having the characteristics of improvedductility, corrosion resistance and high purity. However, as will laterbecome apparent the invention is in no way iimited to this singleexample but on the contrary intended for use in the preparation of manyother metals or alloys, as for example the preparation of titanium,vanadium, hafnium and the like.

Certain special requirements are to be found in apparatus employinghot-wire techniques of metal deposition although the combination ofapparatus in itself is comparatively simple. For example, the entireexposed filament or starting wire, along with the metal depositedthereon, must at all times remain at a temperature above thedecomposition temperature of the decomposable compound, which in thecase of zirconium iodide is about 1300-1500 C. depending upon the typeof crystal growth desired in the deposited material. perature the amountof current supplied to the Wire and its deposit continues to increase asthe deposit grows. As a consequence, the likelihood of considerable heatbeing conducted away from the ends of the hot wire and its deposit tothe electrode, or to an intermediate element between the electrode andhot wire, is thus enhanced. However, if excessive heat flow thus takesplace at the ends of the hot wire the wire may fall below thedecomposition temperature at that point, whereupon the gas liberatedfrom the decomposable compound, in the illustrative example, iodine,will then attack the deposit at this cooler end of the wire. In a shorttime the wire at this point will start to fuse since as more current issupplied to maintain the decomposition temperature at the other parts ofthe wire and its deposit, this particular cooled portion of the wirewill have insufficient current carrying capacity.

A further requir ment is that the filament arran ement must permit ofthe deposit of sufficient material at its ends as well as along thefilament, to carry a very high current especially at the latter stagesof growth of the deposit.

Furthermore, in View of the desirability oi.

In order to maintain this tem- 1 maximum efficiencyof both the vacuumapparatusand the meansemployedfor heating the metal compound to itsvaporization temperature prior to the decomposition step, as well as theadvantages resulting from production of large diameter bars of depositedmaterial, a requirement exists for apparatus which can consistentlyproduce bars of one inch diameter orlarger. To illustrate the probleminvolved in preparing thissize of bar it will be noted that a current ofapproximately 1800 amperes is needed to maintaina one inch diameter barat a temperature sufficient to decompose zirconium iodide vapor on theouter surface thereof.

In addition, a further requirement resides in providing a suitablemechanical mounting :to withstand the weight of the heavy bar depositand without compromising the solution already provided by the inventionfor the other requirements.

Still another requirement is the provision of a combination of apparatusin which suitable maintenance of the electrodes and ready attachment ordetachment of the filament and deposited bar thereto or therefrom can bereadily carried out.

Accordingly, the present invention has as an object the provision of anew and improved apparatus for solving the above-mentionedrequirementsin the art of precipitation of metals by thermal decomposition methods.

Other objects and advantages of the invention will become apparent whenconsidered in connection with the following description and theaccompanying drawings wherein,

Figure 1 is a view, partly in section, showing a vessel in which thermaldecomposition of a metal compound for hot wire deposition of the metalmay be carried out using the improved apparatus of my invention.

Figure 2 is an elevation view of one form of improved hot-wire tipembodying the invention.

Figure 3 is a top plan view of the tip shown in Figure 2.

Figure 4 is a sectional elevation View of the tip shown in Figure '2 andshowing one arrangement for mounting a starting wire upon the tip.

Figure 5 is a sectional elevation View of the tip shown in Figure 2 andshowing a second arrangement for mounting a starting wire upon the tip.

Referring now to Figure l, a suitable vessel or reaction chamber I0,having an associated heating means H, is provided for containing thevapor of the metal compound. A conduit 12 leading to an evacuating meansand a flanged 3 lid I3 of the vessel preferably are employed to the endthat a desired metal compound may be placed within said vessel, andcontaminating air may thereafter be drawn out of said vessel prior tothe formation of the vapor resulting from externally applied heat, allin the manner known in the art. As will be apparent to those skilled inthis work, certain standard precautions will be observed in carrying outthe process, especially in view of the highly corrosive nature of theliberated gas evolved from the metal compound. The material used inconstruction of vessel and other exposed apparatus will accordingly beselected with this feature in mind.- For example in the cyclic iodideprocess of preparing ductile zirconium, the zirconium to be depositedtogether with a small amount of iodine or zirconium iodide may be loadedinto vessel H1, or into a cracking bottle which can be broken afterbeing enclosed in the vessel. After suitable evacuation of the vesselthe heating means ll may be operated'to cause a zirconium iodide vaporto permeate the vessel. Thereafter the hot-wire filament, later to bedescribed, is raised to a suitable temperature and the volatilezirconium tetraiodide will decompose on that wire leaving a deposit ofelemental zirconium and liberating the elemental iodine. This iodine inturn diifuses back to the crude zirconium material, forms more of themetal iodide which in turn diffuses to the wire and is decomposed. Inthis way the seed filament or wire hasbuilt upon it a heavy deposit ofzirconium provided it can be supported on the electrodes and canconstantly receive enough current to remain above the decompositiontemperatureof the metal compound vapor.

For carrying out this type of process there is mounted within the lid 43two massive electrodes M; and is suitably insulated from the vessel andhaving heavy leads iii and I1 respectively ccnnected thereto. Theseleads which may be called upon to carry currents in the order of 2000amperes, or greater, are suitably connected to a regulated source ofelectrical current permitting an appropriate increase in the flow ofcurrent as the deposited metal increases within the vessel, thereby topermit the maintenance of such deposited metal at an appropriatetemperature.

A starting wire or filament 20, also known as a hot-wire, is suspendedwithin the space of the vessel and in accordance with my invention isconnected at its ends to the respective electrodes by means of thedetachable electrode tips 2! and 22. This wire preferably is of a smalldiameter,

in one instance of satisfactory usage being 0.080

inch diameter, and may be either of the same material as the metal to bedeposited, or of a different material than the metal to be deposited aswhenever an alloyed final product is permissible.

As shown in Figures 2 and 3, a preferred form of electrode tip mayconsist of a tapered solid metal member having an enlarged head portion2! and a reduced tail portion 22 and with a centrally disposed aperture23 therethrough. The enlarged head portion is adapted to contact theelectrode with a large surface of contact thus permitting an efiicientiiow of heat by conduction when large electric currents are passingthrough the assembly. The tapered tail portion preferably terminates ina reduced outside diameter which is less than twice the diameter of thestarting wire or of the aperture 23 through which such wire may bepassed. In this way the conduction of heat from the wire to the tip atthis critical point of connection is limited and no appreciable coolingof the wire at this point can take place. While the outside diameter ofthe tail portion may vary with the types of material employed and shouldnot exceed twice the diameter of the wire I have actually found thatbetter results are assured when its diameter actually approaches that ofthe wire. For example, in using a wire of 0.08 inch diameter, an outsidediameter of about 0.10 to 0.103 inch has been found to give excellentresults. Also, in order to insure a good mechanical support for thedeposit of heavy metal upon the wire, means are provided for a rigid butdetachable mounting of the electrode tip upon such electrode. One formof means which has proven satisfactory consists of a'plurality ofadjustable set screws 26 adapted to pass through the lower portion ofthe electrode and engage with a circumferential groove 25 contained onthe periphery of the enlarged head of the tip member. Other means ofdetachably connecting the electrode tip to the electrode however may beused as desired without departing from the invention.

In order to connect the starting wire to the tip various arrangementsmay be employed provided the conduction of heat from the wire to the tipis suitably limited. For example, as shown in Figure 4, a loopedconnector wire 30 may be positioned within aperture 23 with its ends 3|and 32-2 anchored into suitable grooves at the top oi the tip head andwith the closed loop end of the connector extending a short distanceoutwardly of the tail of the electrode tip. Starting wire 2t may then bejoined to the connector by having the loop 33 pass through a small holein the end of the wire, by use of a small separate ring, or by otherequivalent means.

In an alternate arrangement shown in Figure 5 the starting wire 20 maybe positioned in aperture 23 and the end 4| thereof may be anchored in agroove at the head of the tip.

With the apparatus employed as above described the process of depositingmetal may then be carried out without being subject to the disadvantagescommon to the previous practices. For example, as the vessel it! becomesfilled with a vapor of the metallic compound and the bare wire 20 isheated above the decomposition temperature of that vapor, the metalstarts to deposit on all of the surface of the hot wire and a rod-likebar of deposited metal starts to grow. The junction of the wire and thetail of the electrode tip is soon covered with such deposit and as theprocess continues this deposit progressively forms along the taperedtail portion of the tip thus providing an increased current carryingdeposit. Through leads l6 and I! a constantly increasing supply ofcurrent is supplied in order to keep the entire deposit of metal at atemperature above the decomposition temperature and the heat thuscreated may flow to the electrodes through the larger areas provided bythe head of the tapered tips. The possibility of the end of the hot wirethus becoming fused and melted away due to carrying too much heat at anystage of the process is thus eliminated.

It has been found that refractory metals such as molybdenum, tantalum,titanium, tungsten, zirconium, hafnium and the like, as well asgraphite, are especially suited for use in forming the tip member andthe connector wire 30. In general, any refractory metal which does notalloy with the metal being deposited at the temperature of depositionmay be employed. If desired the entire tip may be made of the samematerial as that composing the starting wire 20, or as that of the metalbeing deposited, or both.

After the deposited bar of metal has been grown to the desired size theheater Il may be disconnected, the supply of current to the electrodesmay be discontinued and the lid 13 of the vessel may be removed.Normally, the gas, such as iodine, will at this time be deposited as asolid upon cooler portions of the vessel. By loosening screws 24 thetips and metal deposit may be disconnected from the apparatus andremoved for further processing, while a new Wlle and tip may be replacedon the electrodes, a new charge of material may be added to the vessel,and the lid replaced upon the vessel for a subsequent cycle of metaldeposition.

Various changes in construction and materials of the tips and attachedwire may be made without departing from the scope of the invention andit is not desired to limit my invention to the exact details as shownexcept insofar as defined in. the following claims.

What is claimed is:

1. In combination, a vessel adapted to contain a thermally decomposablevapor of a metal compound, electrodes having a cavity in the end thereofmounted within said vessel, a starting Wire adapted to be maintained ata temperature above the decomposing temperature of said vapor by acurrent supplied to said electrodes, and demountable electrode tip meansfor attaching the ends of said wire to said electrodes, said meanscomprising an enlarged head portion adapted to be mounted in theelectrode cavity and having a recessed surface, a tail portion having adiameter not more than twice the diameter of said wire, retaining meansadapted to engage the electrode and the recessed surface and anintermediate tapered tip portion connecting said head and tail portionsto provide said means with a tapered configuration with the point ofwire attachment thereto being at the tail portion of said means, therebyto insure the maintenance of the temperature at the ends of said wireabove said decomposing temperature by limiting the flow of heat byconduction from the ends of the hot wire to the adjacent electrodes.

2. A tapered electrode tip suitable for detachable mounting upon acooperating electrode and having a head portion of relatively large heatconducting capacity and diameter and a tail portion of relatively smallheat conducting capacity and diameter, said portions being provided withan aperture extending centrally therethrough and adapted to house themounting means for a relatively small hot Wire filament the head portionhaving a recessed surface for use with a separate detachable fasteningmeans engageable in the electrode and recess.

3. An article as defined in claim 2, wherein said head portion isprovided with means for anchoring the end of a hot wire filamentextending through said aperture from the open end of said tail portion.

4. An article as defined in claim 2 wherein said head portion includesmeans for anchoring a separate connector extending through said aperturefrom the open end of said tail portion and connected to the end of afilament at a point spaced from said tail portion.

5. A tapered electrode tip suitable for detachable mounting upon acooperating electrode and being composed of a refractory metal andhaving a head portion of relatively large heat conducting capacity anddiameter and a tail portion of relatively small heat conducting capacityand diameter, said portions being provided with an aperture extendingcentrally therethrough and adapted to house the mounting means for arela tively small hot wire filament whose diameter is not more thanone-half the diameter of said tail portion, the head portion having arecessed surface for use with a separate detachable fastening meansengageable in the electrode and recess.

6. An article as defined in claim 5, wherein said tip consists ofmolybdenum.

'7. An article as defined in claim 5, wherein said tip consists oftantalum.

8. An article as defined in claim 5, wherein said tip consists oftungsten.

9. An article as defined in claim 5, wherein said tip consists ofzirconium.

10. An article as defined in claim 5, wherein said tip consists ofhafnium.

ZALMAN M. S'HAPIRO.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,710,747 Smith Apr. 30, 1929 2,304,834 Lenz Dec. 15, 19422,551,341 Scheer et a1. May 1, 1951

